Re: [asa] Exaptation

From: Nucacids <nucacids@wowway.com>
Date: Wed Jun 24 2009 - 00:10:49 EDT

Bill,

I think you are correct to focus on the necessity of "small incremental
changes" as Darwin himself thought this was an essential component of his
theory (for the reasons you outline).

It is also worth noting that an appeal to exaptation is an attempt to root
the appearance of design in chance, so I think you are on target viewing
that in the context of the need for small incremental changes. And yes,
exaptation is invoked as something that does a lot of heavy lifting in
evolution, as it is the only plausible way to account for the origin of IC.

I would add a couple of points. Exaptation can be viewed as a
non-teleological re-framing of a more traditional concept with clear
teleological echoes - preadaptation. And preadaptation is something that
follows from the front-loading of evolution. I explain this here:

http://designmatrix.wordpress.com/2009/05/28/front-loading-and-preadaptation/

I would also point out that exaptation/preadaptation is rather common at the
molecular level, as it is becoming increasingly clear that many proteins
often have more than one function. Scientists refer to this as
"moonlighting." I raise several examples in my book. Here is one:

"Consider a protein known as platelet-derived endothelial cell growth factor
( PD-ECGF). This protein is an extra-cellular protein, meaning it is
produced in the cell, but exported outside the cell to fulfill its function.
It is classified as a growth factor (it promotes the growth and development
of other cells) and its basic biological function is listed as "cellular
communication and signal transduction."33 In humans, it is expressed in the
liver, placenta, the lining of the uterus, skin cells, and platelets
(specialized cells that circulate in the blood and help clot the blood when
needed). PD-ECGF specifically functions as a signal to stimulate blood
vessel growth and maintenance of the blood vessel linings. How in the world
could you design PD-ECGF and place it in a uni-cellular organism without
having it mutate into oblivion before blood vessels evolved? PD-ECGF is
actually a common metabolic enzyme known as thymidine phosphorylase, found
in eubacteria, archaebacteria, and eukaryotes.34 The enzyme plays a basic
housekeeping role in modifying the nucleotides used by DNA. It is a little
over 300 amino acids in length and 46 percent of the positions contain the
same amino acids in the proteins from E. coli and humans (another mid-level
information protein). The solution in this case is simple. Express the
protein inside the cell and it functions in the metabolism of nucleotides.
Express it outside the cell and it can act as a signal to promote the growth
of blood vessels. Since all cells require nucleotides, PD-ECGF's potential
activity has always been

with life."

And another:

"Consider gephyrin, a protein that is expressed in the lungs, kidneys,
liver, spinal cord, and brain.38 Its function in the brain is well-known,
where it anchors various receptors involved in the transmission of signals
between brain cells. Gephyrin itself is a protein that is inserted into the
membrane and can interact not only with other receptors, but also various
components of the cell's cytoskeleton. Gephyrin also functions as an enzyme
that synthesizes something known as the molybdenum co-factor (Moco), an
important component of many diff erent metabolic enzymes."

And I could go on and on.

Such multifunctionality, coupled with gene duplication, lends support to the
hypothesis that evolution was indeed front-loaded with an assembly of
preadaptations.

Or at the very least, to the fact that proteins are an amazing design
material. ;)

-Mike

----- Original Message -----
From: "Bill Powers" <wjp@swcp.com>
To: <asa@calvin.edu>
Cc: <wjp@swcp.com>
Sent: Tuesday, June 23, 2009 12:14 AM
Subject: [asa] Exaptation

> I'm continuing to think about Irreducible Complexity. A closely related
> concept is that of exaptation, wherein some biological structure or
> process
> used for one function is later used for a different function.
>
> Exaptation is apparently a well accepted doctrine and there a few
> carefully
> documented arguments to support the notion, including the development from
> the
> jaw bone for use in the middle ear, the bone spur of the panda developing
> into
> a thumb, and the development of feathers from thermal insulation into
> feathers
> for flight. The last two have problems in my mind conceptually, the first
> is
> perhaps the best.
>
> Nonetheless, exaptation appears to present theoretical problems, and here
> is why.
>
> It appears to me that Darwinian (random) evolution, not only presumes, but
> must be committed to a principle of incrementalism, whereby evolution
> sensibly
> proceeds according to small incremental changes.
>
> This principle appears necessary because of the random nature of the
> process.
> Significant, but random, changes are highly likely to be deadly, producing
> a
> non-survivable species. This is because it is likely that survival large
> changes are likely to be complex and highly integrated, but to expect a
> random
> process to be able to accomplish such a feat seems to ask far too much.
> On
> the other hand, small changes are more likely to leave the species still
> survivable. Such changes, while small, can be mildly advantageous,
> neutral,
> or even mildly disadvantageous.
>
> The principle of incrementalism presumes that in some sense that changes
> are
> near each other. But this nearness is not conceptual nearness, something
> utterly foreign to a blind process, but probablistic.
>
> Prima facie, exaptation violates this principle of incrementalism. This
> is so
> because the previous function is not probabilistically near the new
> function.
> It is conceptually near perhaps, but how can it be probabilistically near?
>
> Functionality is conceptual. I don't know how else to say it. In a sense
> the
> very notion of functionality is suspicious in a non-teleological process.
> But
> what then do we mean when we say in exaptation that an old function is
> used
> for a new one?
>
> To take, but one example, if one reviews, even in cartoon form the
> evolutionary development of the jaw bone into the middle ear, it appears
> to me
> to be miraculous if viewed as a random process. It only seems reasonable
> "conceptually," but not, to me, as a blind process.
>
> Can anyone help?
>
> thanks,
>
> bill
>
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Received on Wed Jun 24 00:11:39 2009

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